Digital mobile communication systems for voice, such as the Global System for Mobile Communications (GSM) and Digital Advanced Mobile Systems (DAMPS) have expanded very quickly in recent years. Systems for data, such as the GPRS and Enhanced Data rate for GSM Evolution (EDGE) and Universal Mobile Telecommunications System (UMTS), are being developed rapidly, as wide acceptance of the Internet creates a substantial demand. Voice over the fixed packet switched network is being developed and it is expected that there will be an increasing volume of voice traffic using Internet Protocol (IP) networks. Potential demand for voice services over GPRS/Enhanced GPRS (EGPRS)/EDGE is expected to increase.
In GPRS and EGPRS/EDGE, in current arrangements, a Radio Link Control/Medium Access Control (RLC/MAC) block is interleaved over four Time Division Multiple Access (TDMA) bursts in four consecutive time frames. Consequently the USFs are also interleaved over four TDMA bursts, and a USF field cannot be decoded until all four TDMA bursts are received. This leads to a twenty millisecond USF field decoding delay, which in a voice service may not be acceptable.
It has been proposed in a co-pending patent application of the current applicant that one or more USF fields can be sent in one RLC/MAC block in the downlink, depending on the scheme to transmit such blocks. It has also been proposed in another co-pending application of the current applicant that the USF fields are transmitted only in the first burst, so that the polling algorithm is optimized and the mobile reply time is reduced. If the mobile reads its own USF in the first burst, then in the same twenty millisecond period (if the mobile is active) the mobile sends a voice packet on the corresponding uplink traffic channels. Unfortunately, when the USF fields are moved to the first burst, the interleaving depth_is reduced from four bursts to one burst. This degrades the BLock Error Rate (BLER) of the USF by about six dB.
This is illustrated in FIG. 1 which is a plot of the BLER of the USF against Eb/No using block code (36, 3); Typical Urban (TU) 50 is used and there is no Frequency Hopping (FH). The line E on FIG. 1 is a plot for a four burst interleaving in EDGE 8 PSK (Phase Shift Key) and the line V is a plot for voice over EDGE 8 PSK with one burst interleaving. The loss of about 6 dB is clear.